The past decade has seen the introduction of non-detachable couplings for fluid conduits. This has been especially true in aerospace and aircraft applications where maintenance of structural integrity is of utmost concern. The problem that is addressed is that with detachable couplings in addition to the weight penalty of large coupling nuts and unions needed for thread integrity there is always the likelihood of inadvertent uncoupling slight or complete, overtorqued assembly with consequent seat damage of the sealing portions, and a need to inspect the coupling elements for potential fatigue failures or defects in manufacture.
In addressing these problems the prior art has attempted to utilize permanent type fittings joined together as by brazing, welding, silver soldering and mechanical swaging. This invention will be principally concerned with improving the latter but its teaching will be equally applicable to prior art bonded couplings.
U.S. Pat. Nos. 3,474,519 and 3,848,451 show mechanical swaging tools and couplings made thereby. Another noted prior art coupling akin to that of this invention is disclosed by U.S. Pat. No. 3,556,567. These permanent couplings and others known to be more available in the marketplace such as those using the Aeroquip braze process and the Raychem Cryofit process have a common fault that limits their applicability. That is these couplings cannot tolerate even the slightest misalignment between the tubes to be coupled thereby. Recent analysis show that operational loadings with any degree of misalignment in prior art couplings have led to accelerated tube failures. This has been attributed to the pre-stress moment created by misalignment and to the additive effect of stresses in the tubing due to vehicle vibrations, etc.
It is, therefore, a principal object of this invention to bring to the art a self-aligning permanent type fitting which does not induce tube failure by assembly of misaligned tubes.